This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application ARRAYED WAVEGUIDE GRATING MODULE AND DEVICE FOR MONITORING OPTICAL SIGNAL USING THE SAME filed with the Korean Industrial Property Office on Jan. 14, 1999 and there duly assigned Ser. No. 845/1999.
1. Technical Field
The present invention relates to an arrayed waveguide grating (AWG) module for monitoring the characteristics of a wavelength division multiplexed (WDM) optical signal for multiple channels without using a special measuring instrument in a wavelength division multiplexing (WDM) system, and to an optical signal monitoring device and method for monitoring a WDM optical signal using the AWG module.
2. Related Art
In a WDM system, where several optical channels are multiplexed and transmitted to one optical cable, the quality of the WDM optical signal must be monitored before the WDM optical signal is optically demultiplexed into channels.
Generally, the optical power, optical wavelength and optical signal-to-noise ratio (OSNR) of an optical signal of each channel must be measured to monitor a WDM multi-channel optical signal. In a WDM optical transmission device, the wavelength deviation of each channel must be accurately controlled since it causes error not only upon transmission of a signal for a corresponding channel, but also upon transmission of signals of channels adjacent to the corresponding channel. Also, control situations must be monitored in real time. Furthermore, the optical power and the OSNR of optical signals may be different for each channel when a WDM optical amplifier is used, so that the power and the OSNR of each channel must be monitored.
U.S. Pat. No. 5,617,234 to Koga et al., entitled MULTIWAVELENGTH SIMULTANEOUS MONITORING CIRCUIT EMPLOYING ARRAYED-WAVEGUIDE GRATING, issued on Apr. 1, 1997 discloses a structure using an AWG and a photodiode array. In Koga ""234, the wavelength of each channel can be monitored, but the temperature of the AWG must be controlled in real time, an optical signal for providing a reference wavelength is separately required, and the optical power and the OSNR of an optical signal cannot be accurately measured. Also, in the WDM optical transmission system, the optical power, the optical wavelength and the OSNR of each channel signal must be able to be simultaneously monitored. However, in the prior art using an AWG, when two arbitrary items among the three measuring items are measured, the remaining item cannot be measured.
The following additional patents are considered to be representative of the prior art relative to the invention disclosed herein but are burdened by disadvantages discussed herein: U.S. Pat. No. 5,136,671 to Dragone, entitled OPTICAL SWITCH, MULTIPLEXER, AND DEMULTIPLEXER, issued on Aug. 4, 1992; U.S. Pat. No. 5,870,216 to Brock et al., entitled SPLITTERLESS OPTICAL BROADCAST SWITCH, issued on Feb. 9, 1999; U.S. Pat. No. 5,671,304 to Duguay, entitled TWO-DIMENSIONAL OPTOELECTRONIC TUNE-SWITCH, issued on Sep. 23, 1997; U.S. Pat. No. 5,978,539 to Davies et al., entitled OPTICAL DEVICE HAVING A TEMPERATURE INDEPENDENT SPECTRAL RESPONSE USING NONPLANAR GEOMETRIC DISTORTION OF A SUBSTRATE, issued on Nov. 2, 1999; and U.S. Pat. No. 5,986,782 to Alexander et al., entitled SIGNAL-TO-NOISE MONITORING IN WDM OPTICAL COMMUNICATION SYSTEMS, issued on Nov. 16, 1999.
An objective of the present invention is to provide an arrayed wavelength grating (AWG) module for monitoring a wavelength division multiplexed (WDM) multi-channel optical signal in a wavelength division multiplexing (WDM) optical transmission system.
Another objective of the present invention is to provide a device and method for measuring not only the wavelength, optical power and optical signal-to-noise ratio (OSNR) of each channel signal of a WDM multi-channel signal, but also the optical spectrum with respect to an overall optical signal wavelength band.
To achieve the first objective of the invention, there is provided an arrayed waveguide grating (AWG) module which includes: an input waveguide for receiving a wavelength division multiplexed (WDM) optical signal via an optical signal transmission medium; a first star coupler for splitting the power of the WDM optical signal received from the input waveguide, and for transmitting the split optical signals to the waveguides of an AWG unit; an AWG unit for processing the split optical signals output by the first star coupler so that the split optical signals have phase differences which are proportional to the difference between the lengths of the waveguides included in the AWG unit; a second star coupler for focusing the optical signals received from the AWG unit on different locations by causing mutual interference between the received optical signals; and an optical power measurer directly connected to the second star coupler for generating electrical signals dependent on the power values of the optical signals output by the second star coupler.
To achieve the second objective of the invention, there is provided a device and method for monitoring a wavelength division multiplexed (WDM) optical signal. The device includes: an AWG module for receiving the WDM optical signal, for splitting the WDM optical signal into optical signals for different channels, and for converting the split optical signals into electrical signals; an analog-to-digital converter for converting the electrical signals into digital signals; and a data processor for processing the digital signals to analyze the characteristics of the received optical signals.